Authenticating a user subvocalizing a displayed text

ABSTRACT

A computing device for authenticating a user is provided. The computing device is operative to display a first text to the user, acquire a representation of the user subvocalizing a part of the first text, derive a user phrasing signature from the acquired representation, and authenticate the user in response to determining that the user phrasing signature and a reference phrasing signature fulfill a similarity condition. Optionally, the computing device may be further operative to determine if the user is authorized to read the first text. Further optionally, the computing device may be operative to reveal obfuscated parts of the first text in response to determining that the user is authorized to read the first text, or to discontinue displaying the first text, or to obfuscate at least part of the first text, in response to determining that the user is not authorized to read the first text.

TECHNICAL FIELD

The invention relates to a computing device for authenticating a user ofthe computing device, a method of authenticating a user of a computingdevice, a corresponding computer program, and a corresponding computerprogram product.

BACKGROUND

Many types of documents, such as any proprietary information,documentation of unpatented technology, legal or business documents,oftentimes require a solution for controlling who can access theirinformation, i.e., whether a person is authorized to read a certaindocument. Typically, this situation occurs when a user accesses adocument through a computing device, such as a computer, a tablet, or asmartphone. Currently, such documents are typically protected bypasswords or PIN codes, or solutions relying on security cards. Alsoknown are systems relying on biometric information.

Password authentication relies on verification of a user by comparisonof a remembered word or a string of characters, the password orpassphrase, against a version stored with the protected document or in adatabase.

Authentication based on security card systems, often combined with PINs,relies on the user carrying a unique card which is required whenaccessing a protected document through a computing device.

Static biometric identification is the verification of a user bycomparison of unique biological information, such as iris patterns orfingerprints, against reference stored information. These can be usedfor single-challenge or continuous authentication (“Physical AccessProtection using Continuous Authentication”, by R. H. C. Yap, T. Sim,and G. X. Y. Kwang, 2008 IEEE Conference on Technologies for HomelandSecurity, pages 510-512, IEEE, 2008).

Behavioral biometric identification utilizes pattern analysis softwarefor recognizing user specific behavior or device interaction signatures,which may be used for authenticating a user based on use patterns whiletyping on a keyboard (“Keystroke dynamics authentication forcollaborative systems”, by R. Giot, M. El-Abed, and C. Rosenberger,International Symposium on Collaborative Technologies and Systems (CTS'09), pages 172-179, IEEE, 2009) or controlling a touch-baseduser-interface (“Continuous mobile authentication using touchscreengestures”, by T. Feng, Z. Liu, K.-A. Kwon, W. Shi, B. Carbunar, Y.Jiang, and N. Nguyen, 2012 IEEE Conference on Technologies for HomelandSecurity, pages 451-456, IEEE, 2013).

It is also known to authenticate users based on eye tracking technology(“Exploiting Eye Tracking for Smartphone Authentication”, by D. Liu, B.Dong, X. Gao, and H. Wang, Applied Cryptography and Network Security,volume 9092 of the series Lecture Notes in Computer Science, pages457-477, Springer, 2015). Such solutions also provide the possibility totrack and ensure that text has actually been read, either based onelectrooculography (“Robust Recognition of Reading Activity in TransitUsing Wearable Electrooculography”, by A. Bulling, J. A. Ward, H.Gellersen, and G. Tröster, Proceedings of the 6th InternationalConference on Pervasive Computing, pages 19-37, Springer, 2008) or videomethods (“Exploiting Eye Tracking for Smartphone Authentication”, by D.Liu, B. Dong, X. Gao, and H. Wang, Applied Cryptography and NetworkSecurity, volume 9092 of the series Lecture Notes in Computer Science,pages 457-477, Springer, 2015). This may, e.g., be desirable for certaindocument types, such as medical instructions or legal documents.

The known solutions for controlling access of users of a computingdevice to protected documents have numerous disadvantages. For instance,user authentication systems relying on passwords suffer from securityweaknesses such as data breaches or brute force guessing. In addition,passwords are easily forgotten by users, which introduces additionalsecurity issues from repeated use of the same passwords, manual storageof passwords, and security issues associated with password reset orrecovery systems. Moreover, the rise of small and simple keyboards onsmartphones and portable devices also reinforces the use of simplepasswords as users favor brevity due to increased effort in typing.

Authentication systems relying on static biometric information arevulnerable to data breaches and have the disadvantage that once thebiometric data has been compromised it is difficult to change, and thatparticular biometric is no longer useful in an authentication scheme.

Authentication systems which are based on behavioral biometrics providean increased level of security, as user patterns in keystrokes or touchgestures are more difficult to steal or reproduce than fingerprints oriris patterns. They do, however, rely on particular interactions of theuser with a computing device, such as typing on a keyboard or using atouch-based user-interface, and cannot be utilized for user activitiessuch as reading text. Accordingly, they cannot be utilized forcontinuous authentication of a user reading text, e.g., a confidentialdocument.

SUMMARY

It is an object of the invention to provide an improved alternative tothe above techniques and prior art.

More specifically, it is an object of the invention to provide animproved authentication of a user of a computing device while readingtext which is displayed by the computing device. In particular, it is anobject of the invention to provide an improved continuous authenticationof the user.

The text may, e.g., be a protected document, or a part thereof. In thepresent context, a protected document is a document with limited readaccess, such as a legal document, a business document, a documentcomprising technical information, e.g., unpatented technology, and thelike.

These and other objects of the invention are achieved by means ofdifferent aspects of the invention, as defined by the independentclaims. Embodiments of the invention are characterized by the dependentclaims.

According to a first aspect of the invention, a computing device forauthenticating a user of the computing device is provided. The computingdevice comprises processing means which is operative to display a firsttext to the user, acquire a representation of the user subvocalizing atleast a part of the first text, derive a user phrasing signature fromthe acquired representation, and authenticate the user in response todetermining that the user phrasing signature and a reference phrasingsignature fulfill a similarity condition.

According to a second aspect of the invention, a method ofauthenticating a user of a computing device is provided. The method isperformed by the computing device and comprises displaying a first textto the user, acquiring a representation of the user subvocalizing atleast a part of the first text, deriving a user phrasing signature fromthe acquired representation, and authenticating the user in response todetermining that the user phrasing signature and a reference phrasingsignature fulfill a similarity condition.

According to a third aspect of the invention, a computer program isprovided. The computer program comprises computer-executableinstructions for causing a device to perform the method according to anembodiment of the second aspect of the invention, when thecomputer-executable instructions are executed on a processing unitcomprised in the device.

According to a fourth aspect of the invention, a computer programproduct is provided. The computer program product comprises acomputer-readable storage medium which has the computer programaccording to the third aspect of the invention embodied therein.

The invention makes use of an understanding that an improvedauthentication of a user of a computing device in situations when theuser is reading text which is displayed by the computing device, may beachieved based on subvocalization.

Subvocalization is the “internal speech” while reading a text and ischaracterized by minute movements of the larynx and other speechmuscles, as well as other body parts, which are imperceptible to thehuman eye but detectable by technical means. By acquiring arepresentation of the user subvocalizing the text he or she is reading,and deriving a user phrasing signature from the acquired representationwhich subsequently is compared to a reference phrasing signature, theuser can be authenticated while reading the text. The reference phrasingsignature represents the expected phrasing for the user and may bederived from previously acquired representations of the usersubvocalizing text, e.g., during a training or learning phase. Thereference phrasing signature may optionally be updated when thecomputing device is used by the user, i.e., when the user is readingtext displayed by the computing device. To this end, the user isauthenticated based on his or her phrasing when reading text, i.e.,cadence, duration of syllables, and durations of pauses which arerelated to punctuation marks. Typically, the phrasing when reading textis individual for each user, as there are differences in subvocalactivity between users, reading speed, general lexical knowledge, e.g.,the knowledge of irregular words and/or how to pronounce them, theknowledge of words related to a field of expertise, and languageproficiency.

Embodiments of the invention are advantageous since people increasinglyprefer reading documents which are displayed by a computing device,either on a built-in screen or an external screen, rather than a printedpaper copy. The computing device may, e.g., be a mobile phone, a mobileterminal, a smartphone, a tablet, a laptop, an e-book reader, atelevision, or a media player, which typically are provided withbuilt-in screens, oftentimes of touchscreen type. Alternatively, thecomputing device may be a personal computer which is operativelyconnected to an external a computer display.

Advantageously, embodiments of the invention enable continuousauthentication, i.e., they allow to continuously, or at regular orirregular intervals, verify the identity of the user. The user isauthenticated in response to determining that the user phrasingsignature and the reference phrasing signature fulfill a similaritycondition. This is similar to authentication schemes based on biometricauthentication, e.g., involving fingerprints, voice recognition, irispatterns, or behavioral biometric identification, which all rely oncomparing a sample or behavioral pattern obtained from the user andassessing whether the obtained sample or behavioral pattern is insufficient agreement with a reference sample or a reference behavioralpattern, respectively.

According to an embodiment of the invention, the representation of theuser subvocalizing at least a part of the first text is acquired byacquiring nerve signals captured from a throat of the user subvocalizingthe part of the first text, and deriving the representation of the usersubvocalizing at least a part of the first text as a representation ofthe nerve signals. The nerve signals are acquired from one or moresensors, or electrodes, operatively connected to the computing device,in particular electromyographical (EMG) sensors or electrodes. As aperson reads a text, even without vocalizing it audibly, they still makea variety of internal and external motions which are triggered by nervesignals controlling the muscles of the person. Both the nerve signalsand the resulting motions, which typically are imperceptible to thehuman eye, are correlated with the text and can be detected. Inparticular, a single subvocal movement has strong correlations to asingle syllable, and the number of syllables per word can be detected bymeasuring the speed of subsequent subvocal movements. Moreover, whenthey follow each other with a speed above a certain threshold, thisindicates that the subsequent movements belong to the same word. Whenthe detected subvocal activity is below a certain threshold, it can beconcluded that the user makes a pause since he or she has reached apunctuation mark in the text. These internal and external motionsinclude muscle movements which are related to the ones the person wouldmake to audibly create the sounds, such as the movement of vocal chords,and may also include associated movements the person would make, e.g.,sway due to the music and modified breathing patterns. Examples of thesemotions are motions of vocal chords, lips, tongue, jaw, neck, other bodyparts such as heads and shoulders, and motions related to breathing.

According to another embodiment of the invention, the representation ofthe user subvocalizing at least a part of the first text is acquired byacquiring a video sequence of the user subvocalizing the part of thefirst text, magnifying motions of one or more body parts of the user,and deriving the representation of the user subvocalizing at least apart of the first text as a representation of the magnified motions. Themotions of the one or more body parts are correlated with thesubvocalized part of the first text. The representation of the magnifiedmotions may, e.g., be derived using one or more metrics quantifying themotions of the lips, throat, or other body parts, of the user. The videosequence is acquired from a camera operatively connected to thecomputing device, e.g., a camera which is comprised in the computingdevice, such as a front-facing camera in a smartphone or tablet.Alternatively, an external camera, such as a web cam which is connectedto the computing device via an interface may be used. The cameracaptures motions of the one or more body parts of the user, such as theuser's lips, throat, mouth, nose, face, neck, or shoulders. The motionsmay, e.g., be magnified by means of Eulerian Video Magnification (EVM)or Lagrangian techniques which are described in further detail below.Acquiring the representation of the melody subvocalized by the user bymeans of a video capturing the user subvocalizing the melody, andprocessing the video to magnify motions which are correlated with thesubvocalized text, is an alternative to utilizing EMG sensors forcapturing nerve signals.

According to an embodiment of the invention, the user phrasing signatureis derived from the acquired representation by identifying syllables andpauses in the acquired representation, determining respective durationsof the identified syllables and pauses, and deriving the user phrasingsignature as a sequence of the determined durations of the syllables andpauses. That is, the acquired representation is transformed into asignal, or a time-dependent function, representing the phrasing of thesubvocalized first text, or a part thereof.

According to an embodiment of the invention, the reference phrasingsignature is derived by identifying syllables and pauses in the firsttext, acquiring reference durations of syllables and pauses, andderiving the reference phrasing signature as a sequence of the referencedurations of the identified syllables and pauses. Preferably, thereference durations of syllables and pauses are derived from acquiredrepresentations of the user subvocalizing text by identifying syllablesand pauses in the acquired representations, determining respectivedurations of the identified syllables and pauses, and storing thedetermined durations of syllables and pauses as the reference durationsof syllables and pauses. Advantageously, the reference durations may bederived from previously acquired representations of the usersubvocalizing text, e.g., during a learning or training phase.Optionally, the reference durations of syllables and pauses, andconsequently the reference phrasing signature, may be dependent on atype of text. This is advantageous in that user subvocalizationtypically depends on the type of the first text, since people tend toread different types of texts with different phrasing. For instance,technical or legal texts are oftentimes read more carefully, andconsequently slower, than, e.g., news articles.

According to an embodiment of the invention, it is determined that theuser phrasing signature and the reference phrasing signature fulfill asimilarity condition by calculating a correlation between the userphrasing signature and at least a consecutive part of the referencephrasing signature, and determining that the user phrasing signature andthe reference phrasing signature fulfill the similarity condition if thecalculated correlation exceeds a first threshold value. The consecutivepart of the reference phrasing signature corresponds to the part of thefirst text which is subvocalized by the user. The first threshold valuemay be configured either by the user, a manufacturer of the computingdevice, or a provider of a software application or a service relying onuser authentication in accordance with embodiments of the invention, andreflects a measure of correlation between the user phrasing signatureand the part of the reference phrasing signature which corresponds tothe subvocalized part of the first text, and which is commensurate withestablishing, to a desired certainty, that the user has read andsubvocalized the part of the first text. Optionally, the correlation maybe calculated between the user phrasing signature and the entirereference phrasing signature, and it is further determined that the userhas read the first text substantially in its entirety if the calculatedcorrelation exceeds a second threshold value. Similar to the firstthreshold value, the second threshold value may be configured either bythe user, a manufacturer of the computing device, or a provider of asoftware application or a service relying on user authentication inaccordance with embodiments of the invention, and reflects a measure ofcorrelation between the user phrasing signature and the entire referencephrasing signature, and is commensurate with establishing, to a desiredcertainty, that the user has read the entire first text. Advantageously,this may be used for concluding that the user actually has read thetext, e.g., a legal document, an agreement for using a service providedover the Internet or a computer program, or medical information providedwith a drug, rather than just gazing at it.

According to an embodiment of the invention, it is further determined,in response to authenticating the user, if the user is authorized toread the first text. This is advantageous in scenarios in which thefirst text, and optional further texts which are related to the firsttext, such as legal documents, business documents, agreements, or thelike, e.g., is/are confidential. Typically, only a limited group ofusers is allowed to read such texts. Preferably, it is determined if theuser is authorized to read the first text based on permissioninformation associated with the first text. The permission informationmay, e.g., be encoded as metadata and stored in a document comprisingthe first text, or stored separately in a database.

According to an embodiment of the invention, obfuscated parts of thefirst text are revealed in response to determining that the user isauthorized to read the first text. For instance, some words or parts ofthe first text may obfuscated, e.g., blurred or blocked, when the firsttext is displayed. Once the user is authenticated as a user which isauthorized to read the first text, the obfuscated parts are revealed.

According to an embodiment of the invention, displaying the first textis discontinued in response to determining that the user is notauthorized to read the first text, or in response to determining thatthe user phrasing signature and the reference phrasing signature fail tofulfill the similarity condition. In other words, the first text, whichmay be confidential, is displayed until an attempt to authenticate theuser has failed, or until it has been determined that the authenticateduser is not authorized to read the first text. Alternatively, instead ofdiscontinuing displaying the first text, the first text, or partsthereof, may be obfuscated in response to determining that the usersubvocalization signature and the reference subvocalization signaturefail to fulfill the similarity condition, or that the user is notauthorized to read the first text.

According to an embodiment of the invention, a second text is displayedin response to determining that the user is authorized to read the firsttext. For instance, the first text and the second text may both be partsof a protected document, such as a legal agreement. This is advantageousin scenarios where the first part is not confidential, whereas thesecond part is confidential and is only displayed if the user isauthenticated, while reading the first text, and is authorized to readthe document comprising the first and the second text. Preferably, thesecond text is displayed in response to detecting that the usersubvocalizes a closing part of the first text, i.e., is about to finishreading the first text.

Even though advantages of the invention have in some cases beendescribed with reference to embodiments of the first aspect of theinvention, corresponding reasoning applies to embodiments of otheraspects of the invention.

Further objectives of, features of, and advantages with, the inventionwill become apparent when studying the following detailed disclosure,the drawings, and the appended claims. Those skilled in the art realizethat different features of the invention can be combined to createembodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of theinvention, will be better understood through the following illustrativeand non-limiting detailed description of embodiments of the invention,with reference to the appended drawings, in which:

FIG. 1 shows a computing device for authenticating a user based on atext subvocalized by the user, in accordance with an embodiment of theinvention.

FIG. 2 shows a computing device for authenticating a user based on atext subvocalized by the user, in accordance with another embodiment ofthe invention.

FIG. 3 exemplifies an image of a video sequence captured by a cameracomprised in the embodiment of the computing device shown in FIG. 2.

FIG. 4 illustrates a text, its corresponding phrasing graph, and itscorresponding phrasing signature, in accordance with embodiments of theinvention.

FIGS. 5A and 5B illustrate obfuscating at least parts of the first text,in accordance with embodiments of the invention.

FIG. 6 illustrates displaying a second text, in accordance withembodiments of the invention.

FIG. 7 illustrates displaying a text for authenticating a user, inaccordance with embodiments of the invention.

FIG. 8 shows an embodiment of the processing means comprised in thecomputing device for authenticating a user.

FIG. 9 shows another embodiment of the processing means comprised in thecomputing device for authenticating a user.

FIG. 10 shows a method of authenticating a user of a computing device,in accordance with embodiments of the invention.

All the figures are schematic, not necessarily to scale, and generallyonly show parts which are necessary in order to elucidate the invention,wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

The invention will now be described more fully herein after withreference to the accompanying drawings, in which certain embodiments ofthe invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided byway of example so that this disclosure will be thorough and complete,and will fully convey the scope of the invention to those skilled in theart.

The embodiments of the invention described herein make use of anunderstanding that a user of a computing device can be authenticatedbased on subvocalizing a text he or she is reading. Subvocalization isthe “internal speech” while reading a text and is characterized byminute movements of the larynx and other speech muscles, as well asother body parts, which are imperceptible to the human eye butdetectable by technical means. As a person reads a text, although theydo not make audible noise, they still make a variety of internal (e.g.,vocal chords) and external (e.g., lips) motions which can be detected,albeit being imperceptible to the human eye. These motions includemuscle movements which are related to the ones the person typicallywould make to create audible sounds, and which consequently arecorrelated with the text subvocalized by the user. To give someexamples, the movements include:

-   -   Lip motions: Each time a person says a syllable their lips move.        The pronunciation of each syllable requires the user to move        their lips. For instance, pronouncing the word “sen-tence”        requires to first pronounce “sen” and then again to pronounce        “tence”.    -   Throat movement: The utterance of a syllable also requires the        user to change the shape of their vocal chords. This is done by        moving the muscles that control the vocal chords, and this        movement in turn moves the surface of the user's throat.    -   Pauses: A person who is reading pauses in between words, and        also at punctuation points such as comma, question mark, and        full stop. The person may also breath during a pause, resulting        in modified breathing patterns.    -   Uncertainty: If a person is pronouncing a word they are less        certain about it may take longer as they need cognitive effort        to work out what the word is.

In addition, a person who is reading may also sway to the text he/she isreading, in particular if the text is lyrics of a piece of music orpoetry.

Advantageously, by acquiring a representation of the user subvocalizingthe text he or she is reading, and deriving a user phrasing signaturefrom the acquired representation which subsequently is compared to areference phrasing signature, the user can be authenticated whilereading the text. To this end, the user phrasing signature reflects theuser's phrasing when reading a text, i.e., cadence, duration ofsyllables, and durations of pauses between words as well as pauses whichare related to punctuation marks. Correspondingly, the referencephrasing signature reflects an expected phrasing for which is based onuser-specific information obtained during a learning or training phase.

In FIG. 1, an embodiment 100 of the computing device for authenticatinga user 110 of computing device 100 is shown. Computing device 100 isoperative to authenticate user 110 based on a first text 131 which isdisplayed by computing device 100 and subvocalized by user 110 whenreading first text 131. Computing device 100 is in FIG. 1 illustrated asa tablet comprising a display 101, e.g., a touchscreen, a front-facingcamera 102, processing means 103, a communications module 104, and anoptional interface 105 for connecting external devices, as is describedfurther below.

Communications module 104 is operative to effect wireless communicationswith a Radio Access Network (RAN) or with another computing device,based on a cellular telecommunications technique such as the GlobalSystem for Mobile communications (GSM), Universal MobileTelecommunications System (UMTS), Long Term Evolution (LTE), or any 5Gstandard. Alternatively, or additionally, communications module 104 maybe operative to effect wireless communications through a Wireless LocalArena Network (WLAN)/Wi-Fi network.

Interface 105 for connecting external devices is in FIG. 1 illustratedas a conventional headphone jack, or headset jack, but may alternativelybe embodiment as any other type of connector, such as a Lightningconnector, a Universal Serial Bus (USB) connector, or the like. As yet afurther alternative, interface 105 may also be a wireless interfacebased on technologies like coded visible or invisible light, Bluetooth,or ZigBee.

Computing device 100 is operative to display first text 131 to user 110,either using built-in display 101 or an external display which isoperatively connected to computing device 100, e.g., a computer display.Computing device 100 is further operative to acquire a representation ofuser 110 subvocalizing at least a part of first text 131, and to derivea user phrasing signature from the acquired representation. Computingdevice 100 is further operative to authenticate user 110 in response todetermining that the user phrasing signature and a reference phrasingsignature fulfill a similarity condition.

More specifically, and with reference to FIG. 1, computing device 100 isoperative to acquire the representation of user 110 subvocalizing thepart of first text 131 by acquiring nerve signals which are capturedfrom the throat 111 of user 110 when subvocalizing the part of firsttext 131. The nerve signals may be acquired by means of one or more EMGsensors 120, or electrodes, which are attached to throat 111, e.g., onesensor 120 on each side of the larynx, and which are operativelyconnected to computing device 100, e.g., via interface 105. The capturednerve signals are correlated with the part of first text 131 which user110 subvocalizes when reading, since they control movements of thelarynx and other body parts 111-115 of user 110. The nerve signals whichare acquired from sensors 120 may either be received directly, e.g., asan analog electric signal, as a digitized representation of the analogsensor signal, or as a chunk of data captured by sensors 120 anddelivered to computing device 100, optionally after pre-processing,either wired or wirelessly via interface 105. The representation of user110 subvocalizing the part of first text 131 is derived as arepresentation of the nerve signals, and can subsequently be used forderiving the user phrasing signature, as is described further below withreference to FIG. 4.

In FIG. 2, another embodiment 200 of the computing device forauthenticating a user 110 of computing device 100 is shown. Similar tocomputing device 100 described with reference to FIG. 1, computingdevice 200 comprises a display 101, e.g., a touchscreen, a front-facingcamera 102, processing means 103, a communications module 104, and anoptional interface 105 for connecting external devices.

In correspondence with what is described with reference to FIG. 1,computing device 200 is operative to display first text 131 to user 110,either using built-in display 101 or an external display which isoperatively connected to computing device 200, e.g., a computer display.Computing device 200 is further operative to acquire a representation ofuser 110 subvocalizing at least a part of first text 131, and to derivea user phrasing signature from the acquired representation. Computingdevice 200 is further operative to authenticate user 110 in response todetermining that the user phrasing signature and a reference phrasingsignature fulfill a similarity condition.

In contrast to what is described with reference to FIG. 1, computingdevice 200 is operative to acquire the representation of user 110subvocalizing the part of first text 131 by acquiring a video sequenceof user 110 subvocalizing the part of first text 131, and magnifyingmotions of one or more body parts 111-115 of user 110 which arecorrelated with the subvocalized part of first text 131. The videosequence is acquired from a camera operatively connected to thecomputing device 200, such as front-facing camera 102 or an externalcamera operatively connected to computing device 200, e.g., a web cam ora camera mounted in a computer display. The camera has a field-of-view130 so as to capture at least one of the user's 110 face, throat 111,mouth or lips 112, nose 113, neck 114, and shoulders 115. An example ofan image of a video sequence captured by camera 102 is illustrated inFIG. 3.

More specifically, computing device 200 is operative to magnify themotions of one or more body parts 111-115 by video processing theacquired video sequence, either using EVM or by utilizing Lagrangiantechniques. EVM is an image processing technique which applies a spatialdecomposition followed by a temporal filter to the frames of a standardvideo in order to amplify very small motions which are present buttypically are imperceptible to the human eye. The technique can beapplied in real-time to highlight events occurring at specified temporalfrequencies. For a description of EVM, see, e.g., “Eulerian VideoMagnification for Revealing Subtle Changes in the World”, by H.-Y. Wu,M. Rubinstein, E. Shih, J. Guttag, F. Durand, and W. Freeman(Proceedings of ACM SIGGRAPH 2012, ACM Transactions on Graphics, vol.31, article no. 65, ACM New York, 2012). A comparison between EVM andthe Lagrangian approach has been reported in “Phase-based video motionprocessing”, by N. Wadhwa, M. Rubinstein, F. Durand, and W. T. Freeman(SIGGRAPH 2013 Conference Proceedings, ACM Transactions on Graphics,vol. 32, article no. 80, ACM New York, 2013), and it was concluded thatthe Eulerian approach, i.e., EVM, supports larger amplification factorsat better noise performance. Whereas the Lagrangian approaches estimatethe motions explicitly (so the motions themselves are amplified), EVMrelies on calculating and amplifying the non-motion compensated framedifferences. A solution for coping with large motions in the Lagrangianapproach is reported in “Video magnification in presence of largemotions” by M. A. Elgharib, M. Hefeeda, F. Durand, and W. T. Freeman(2015 IEEE Conference on Computer Vision and Pattern Recognition (CVPR),pages 4119-4127, IEEE Computer Society, 2015), and is based on defininga region-of-interest within which motions are magnified.

Further with reference to FIGS. 2 and 3, computing device 200 isoperative to derive the representation of user 110 subvocalizing thepart of first text 131 as a representation of the magnified motions. Forinstance, the representation may be based on one or more metrics whichquantify the motions of lips 112, neck 114, or other body parts, of user110. In practice, if lips 112 are captured in the video sequenceobtained from camera 102, the representation may be based on a measureddistance 301, magnified by video processing, between the upper and lowerlip 112 over time. As an alternative, the representation may be based ona measured width 302, magnified by video processing, of neck 114 overtime. The representation of user 110 subvocalizing the part of firsttext 131 can subsequently be used for deriving the user phrasingsignature, as is described in the following.

In FIG. 4, a text 401 is illustrated as an example for first text 131.The same text is again illustrated as text 402, with additional markersfor indicating syllables and pauses due to punctuation marks. When readby user 110, text 401 can be represented as a phrasing graph 403 whichgraphically illustrates the phrasing which user 110 applies when readingtext 401. In particular, phrasing graph 403 illustrates the duration ofeach syllable (indicated by “_”), the separation between syllables(indicated by “/”), which is an indication for user 110's readingcadence, as well as the duration of pauses (indicated by “

”) at the commas and the question mark, respectively. Note that whereasphrasing graph 403 is a graphical representation of user 110's phrasingwhen reading text 401, it will be appreciated that the user phrasingsignature, and the reference phrasing signature, may be cast into amathematical representation which is suitable for quantifying acorrelation between the two.

More specifically, computing device 100 or 200 may be operative toderive the user phrasing signature from the acquired representation ofuser 110 subvocalizing the part of first text 131/401 by identifyingsyllables and pauses in the acquired representation, determiningrespective durations of the identified syllables and pauses, andderiving the user phrasing signature as a sequence of the determineddurations of the syllables and pauses. For instance, the user phrasingsignature may be represented by a time-dependent function, or a signal,which assumes a value of one (“1”) during utterance of a syllable byuser 110, and a value of zero (“0”) during a pause between syllables, apause between words, or a pause due to a punctuation mark. An example404 of such a function, corresponding to phrasing graph 403, isillustrated in FIG. 4. It will be appreciated that numerous mathematicalrepresentations of the user phrasing signature and the referencephrasing signature may be envisaged, and the embodiments of theinvention are not limited to the particular form 404 of the phrasingsignature illustrated in FIG. 4.

Correspondingly, computing device 100/200 may be operative to derive thereference phrasing signature by identifying syllables and pauses infirst text 131/401, acquiring respective durations of syllables andpauses, and deriving the reference phrasing signature as a sequence ofthe reference durations of the syllables and pauses. The referencephrasing signature is derived in a correspondence with user phrasingsignature 404 as is described hereinbefore, i.e., as a time-dependentfunction or a signal, and is suitable for calculating the correlationbetween the user phrasing signature and the reference phrasingsignature. The reference durations of the syllables and pauses (betweensyllables or words, and due to punctuation marks) are user specific andconstitute a user-specific subvocalization signature, or a user-specificsubvocalization fingerprint, and may either be acquired from a storage,i.e., a memory, of computing device 100/200, or from an externaldatabase. Preferably, the reference durations of the syllables andpauses are derived by computing device 100/200 during a learning ortraining phase by acquiring representations of user 110 subvocalizingtext. The text may either be displayed by computing device 100/200 orprovided by any other means, e.g., as a printed paper copy. Preferably,the text is composed so as to facilitate deriving of the referencedurations of the syllables and pauses. More specifically, computingdevice 100/200 is operative to identify syllables and pauses in theacquired representations, determine respective durations of theidentified syllables and pauses, and store the determined durations ofsyllables and pauses as the reference durations of syllables and pauses,in a storage comprised in computing device 100/200 or in an externaldatabase. The stored reference durations of syllables and pausesconstitute a user-specific subvocalization signature, or a user-specificsubvocalization fingerprint. Optionally, the reference durations ofsyllables and pauses may be dependent on a type of text. This isadvantageous in that the acquired user subvocalization typically dependson the type of first text 131, since people tend to read different typesof texts with different phrasing. For instance, technical or legal textsare oftentimes read more carefully, and consequently slower, than, e.g.,news articles.

Computing device 100/200 may further be operative to determine that theuser phrasing signature and the reference phrasing signature fulfill asimilarity condition by calculating a correlation between the userphrasing signature and at least a consecutive part of the referencephrasing signature, and determining that the user phrasing signature andthe reference phrasing signature fulfill the similarity condition if thecalculated correlation exceeds a first threshold value.

As is known in the art, correlation is a statistical relationship whichreflects the extent to which two random variables, e.g., twotime-dependent functions or signals, such as the user phrasing signatureand the reference phrasing signature, overlap. The correlation betweentwo random variables is commonly referred to as cross-correlation andcan be quantified by means of a correlation function, which can beexpressed as an integral over the two random variables over time.Typically, correlation functions are normalized such that a perfectcorrelation between the two random variables, i.e., the two randomvariables are identical, result in a maximum value which oftentimes ischosen to be equal to one (“1”). Correspondingly, the correlation of twocompletely independent random variables yields a correlation value ofzero (“0”). An example is the well-known Pearson product-momentcorrelation coefficient.

To this end, the correlation between the user phrasing signature and thereference phrasing signature, which both are represented astime-dependent functions, or signals, is calculated. In the field ofsignal processing, this is also referred to as the sliding dot-productor the sliding inner-product, and is commonly used for searching a longsignal for a shorter feature. For embodiments of the invention, the userphrasing signature is typically shorter than the reference phrasingsignature, as the latter represents the entire first text 131 displayedto user 110, whereas user 110 may have read and subvocalized only a partof first text 131. The subvocalized part of first text 131 may beidentified by “sliding” the user phrasing signature over the referencephrasing signature, i.e., by varying a shift in time between the two, soas to identify the value for the time shift which maximizes thecorrelation between a consecutive part of the reference phrasingsignature having a duration corresponding to that of the derived userphrasing signature, and the reference phrasing signature. The obtainedvalue for the time shift which maximizes the calculated correlation maybe used as an indication of the location in first text 131 where user110 has started reading. Oftentimes, user 110 starts reading at thebeginning of first text 131, but not necessarily.

Optionally, computing device 100/200 may be operative to calculate thecorrelation between the user phrasing signature and the entire referencephrasing signature, rather than a consecutive part of it, and determinethat the user has read the first text substantially in its entirety ifthe calculated correlation exceeds a second threshold value.Advantageously, this can be utilized for determining that a useractually has read a text in its entirety, rather than just glancing atit.

Preferably, suitable values for the first threshold value and/or thesecond threshold value may be obtained during a learning or trainingphase during which user 110 is instructed to subvocalize one or moretexts which preferably are dedicated for the purpose of configuring thefirst and/or the second threshold value. For instance, this may beachieved by using an upper bound, an average value, or any othersuitable value, of correlation values which are observed during thelearning phase. Optionally, the first and the second threshold value maybe equal. It will be appreciated that the values used for the firstand/or second threshold value may be selected based on a required levelof security. To this end, a higher value corresponds to a higher levelof security, as a higher value of correlation between the user phrasingsignature and the reference phrasing signature indicates a higher degreeof similarity between the two.

Optionally, computing device 100/200 may further be operative todetermine, in response to authenticating user 110, if user 110 isauthorized to read first text 131. Preferably, the determination may bebased on permission information associated with first text 131. Thepermission information may, e.g., be encoded as metadata and stored in adocument comprising first text 131, or stored separately in an externaldatabase.

In FIGS. 5A and 5B, a further embodiment 500 of the computing device forauthenticating a user of the computing device is illustrated. Computingdevice 500 is similar to computing devices 100 and 200 describedhereinbefore, but is additionally operative to reveal obfuscated partsof first text 131 in response to determining that user 110 is authorizedto read first text 131. For instance, parts of first text 131 mayinitially be blurred or blocked when first text 131 is displayed, as isillustrated in FIGS. 5A and 5B, respectively. Once user 110 isauthenticated as a user who is authorized to read first text 131, theobfuscated parts are revealed.

Alternatively, or additionally, computing device 500 may be operative todiscontinue displaying first text 131, or to obfuscate at least part offirst text, in response to determining that user 110 is not authorizedto read first text 131, or in response to determining that the userphrasing signature and the reference phrasing signature fail to fulfillthe similarity condition. For instance, parts of first text 131 may beblurred or blocked, as is illustrated in FIGS. 5A and 5B, respectively,in response to determining that user 110 is not authorized to read firsttext 131 or that the similarity condition is not fulfilled. In otherwords, first text 131, which may be confidential, is displayed until anattempt to authenticate user 110 has failed, or until it has beendetermined that the authenticated user 110 is not authorized to readfirst text 131.

Yet another embodiment 600 of the computing device for authenticating auser of the computing device is illustrated in FIG. 6. Computing device600 is similar to computing devices 100, 200, and 500, describedhereinbefore, but is additionally operative to display a second text 132to user 110 in response to determining that user 110 is authorized toread first text 131. Preferably, second text 132 is displayed inresponse to detecting that user 110 subvocalizes a closing part of firsttext 131, i.e., is about to finish reading first text 131. This can beachieved by calculating a correlation between the user phrasingsignature and a trailing part of the reference phrasing signature, anddetermining that a closing part of first test 131 has been read if thecalculated correlation exceeds a threshold value, e.g., the firstthreshold value.

In FIG. 7, yet a further embodiment 700 of the computing device forauthenticating a user of the computing device is illustrated. Computingdevice 600 is similar to computing devices 100, 200, 500, and 600,described hereinbefore, but is additionally operative to authenticateuser 110 when attempting to access, i.e., to log into, computing device700. This may be achieved by displaying first text 131 on a login screendisplayed by computing device 700, and granting access to computingdevice 700 in response to authenticating user 110, as is describedhereinbefore. Preferably, first text 131 may be composed so as toemphasize differences in phrasing between users, e.g., by using specificwords or arrangements of words in composing first text 131.

Whereas computing devices 100, 200, 500, 600, and 700, (in the followingreferred to as 100-700), are in the drawings illustrated as tablets orsmartphones, embodiments of the invention may alternatively be embodiedas a mobile phone, a mobile terminal, a personal computer, a laptop, ane-book reader, a computer display, a television, or a media player.

In the following, embodiments of processing means 103, comprised inembodiments 100-700 of the computing device for authenticating a user ofthe computing device, are described with reference to FIGS. 8 and 9.

In FIG. 8, a first embodiment 800 of processing means 103 is shown.Processing means 800 comprises a processing unit 802, such as a generalpurpose processor, and a computer-readable storage medium 803, such as aRandom Access Memory (RAM), a Flash memory, or the like. In addition,processing means 800 comprises one or more interfaces 801 (“I/O” in FIG.8) for controlling and/or receiving information from other componentscomprised in computing device 100-700, such as display 101, camera 102,communications module 104, and interface 105 for external devices. Inparticular, interface(s) 801 may be operative to acquire, from one ormore sensors 120 operatively connected to computing device 100, nervesignals captured from throat 111 of user 110 subvocalizing a part offirst text 131. Alternatively, interface(s) 801 may be operative toacquire, from camera 102, a video sequence of user 110 subvocalizing apart of first text 131. Memory 803 contains computer-executableinstructions 804, i.e., a computer program, for causing computing100-700 device to become operative to perform in accordance withembodiments of the invention as described herein, whencomputer-executable instructions 804 are executed on processing unit802.

In FIG. 9, an alternative embodiment 900 of processing means 103 isillustrated. Similar to processing means 800, processing means 900comprises one or more interfaces 901 (“I/O” in FIG. 9) for controllingand/or receiving information from other components comprised in thecomputing device, such as display 101, camera 102, communications module104, and interface 105 for external devices. In particular, interface(s)801 may be operative to acquire, from one or more sensors 120operatively connected to computing device 100, nerve signals capturedfrom throat 111 of user 110 subvocalizing a part of first text 131.Alternatively, interface(s) 801 may be operative to acquire, from camera102, a video sequence of user 110 subvocalizing a part of first text131. Processing means 900 further comprises a display module 902, anacquisition module 903, an authentication module 904, and an optionalpermission module 905, which are configured to cause computing device100-700 to perform in accordance with embodiments of the invention asdescribed herein.

In particular, display module 902 is configured to display first text131 to user 110, acquisition module 903 is configured to acquire arepresentation of user 100 subvocalizing at least a part of first text131 and derive a user phrasing signature from the acquiredrepresentation, and authentication module 904 is configured toauthenticate user 110 in response to determining that the user phrasingsignature and a reference phrasing signature fulfill a similaritycondition.

Acquisition module 903 may be configured to acquire the representationof user 110 subvocalizing at least a part of first text 131 byacquiring, from one or more sensors 120 operatively connected tocomputing device 100-700, nerve signals captured from a throat 111 ofuser 110 subvocalizing the part of first text 131, and deriving therepresentation of user 110 subvocalizing at least a part of first text131 as a representation of the nerve signals. Alternatively, acquisitionmodule 903 may be configured to acquire the representation of user 110subvocalizing at least a part of first text 131 by acquiring, fromcamera 102 operatively connected to computing device 100-700, a videosequence of user 110 subvocalizing the part of first text 131,magnifying, by video processing the acquired video sequence, motions ofone or more body parts 111-115 of user 110, which motions are correlatedwith the subvocalized part of first text 131, and deriving therepresentation of the user subvocalizing at least a part of the firsttext as a representation of the magnified motions.

Acquisition module 903 may be configured to derive the user phrasingsignature from the acquired representation by identifying syllables andpauses in the acquired representation, determining respective durationsof the identified syllables and pauses, and deriving the user phrasingsignature as a sequence of the determined durations of the syllables andpauses.

Acquisition module 903 may further be configured to identify syllablesand pauses in first text 131, acquire reference durations of syllablesand pauses, and derive the reference phrasing signature as a sequence ofthe reference durations of the identified syllables and pauses.Optionally, acquisition module 903 may further be configured to derivethe reference durations of syllables and pauses from acquiredrepresentations of user 110 subvocalizing text by identifying syllablesand pauses in the acquired representations, determining respectivedurations of the identified syllables and pauses, and storing thedetermined durations of syllables and pauses as the reference durationsof syllables and pauses. Further optionally, the reference durations ofsyllables and pauses are dependent on a type of text.

Authentication module 904 may be configured to determine that the userphrasing signature and the reference phrasing signature fulfill asimilarity condition by calculating a correlation between the userphrasing signature and at least a consecutive part of the referencephrasing signature, and determining that the user phrasing signature andthe reference phrasing signature fulfill the similarity condition if thecalculated correlation exceeds a first threshold value. Optionally,authentication module 904 may be further configured to calculate thecorrelation between the user phrasing signature and the entire referencephrasing signature, and to determine that the user has read the firsttext substantially in its entirety if the calculated correlation exceedsa second threshold value.

Processing means 900 may further comprise permission module 905 which isconfigured to determine, in response to authenticating user 110 byauthentication module 904, if user 110 is authorized to read first text131. Preferably, permission module 905 is configured to determine ifuser 110 is authorized to read first text 131 based on permissioninformation associated with first text 131.

Display module 902 may further be configured to reveal obfuscated partsof first text 131 in response to determining, by permission module 905,that user 110 is authorized to read first text 131.

Display module 902 may further be configured to discontinue displayingfirst text 131 or to obfuscate at least part of first text 131 inresponse to determining, by permission module 905, that user 110 is notauthorized to read first text 131.

Display module 902 may further be configured to display to user 110 asecond text 132 in response to determining, by permission module 905,that user 110 is authorized to read first text 131. Preferably, displaymodule 902 is configured to display second text 132 in response todetecting that user 110 subvocalizes a closing part of first text 131.

Display module 902 may further be configured to discontinue displayingfirst text 131 or to obfuscate at least part of first text 131 inresponse to determining, by authentication module 904, that the userphrasing signature and the reference phrasing signature fail to fulfillthe similarity condition.

Interface(s) 801 and 901, and modules 902-905, as well as any additionalmodules comprised in processing means 900, may be implemented by anykind of electronic circuitry, e.g., any one, or a combination of,analogue electronic circuitry, digital electronic circuitry, andprocessing means executing a suitable computer program.

In the following, embodiments 1000 of the method of authenticating auser 110 of a computing device are described with reference to FIG. 10,in accordance with embodiments of the invention. An embodiment of method1000 may be performed by a computing device such as a mobile phone, amobile terminal, a smartphone, a tablet, a personal computer, a laptop,an e-book reader, a computer display, a television, or a media player.

Method 1000 comprises displaying 1001 a first text to the user,acquiring 1002 a representation of the user subvocalizing at least apart of the first text, deriving 1003 a user phrasing signature from theacquired representation, and authenticating 1005 the user in response todetermining 1004 that the user phrasing signature and a referencephrasing signature fulfill a similarity condition.

Acquiring 1002 the representation of the user subvocalizing at least apart of the first text may comprise acquiring, from one or more sensorsoperatively connected to the computing device, nerve signals capturedfrom a throat of the user subvocalizing the part of the first text, andderiving the representation of the user subvocalizing at least a part ofthe first text as a representation of the nerve signals. Alternatively,acquiring 1002 the representation of the user subvocalizing at least apart of the first text may comprise acquiring, from a camera operativelyconnected to the computing device, a video sequence of the usersubvocalizing the part of the first text, magnifying, by videoprocessing the acquired video sequence, motions of one or more bodyparts of the user, which motions are correlated with the subvocalizedpart of the first text, and deriving the representation of the usersubvocalizing at least a part of the first text as a representation ofthe magnified motions.

Deriving 1003 the user phrasing signature from the acquiredrepresentation may comprise identifying syllables and pauses in theacquired representation, determining respective durations of theidentified syllables and pauses, and deriving the user phrasingsignature as a sequence of the determined durations of the syllables andpauses.

Method 1000 may further comprise deriving the reference phrasingsignature by identifying syllables and pauses in the first text,acquiring reference durations of syllables and pauses, and deriving thereference phrasing signature as a sequence of the reference durations ofthe syllables and pauses. Preferably, method 1000 further comprisesderiving the reference durations of syllables and pauses from acquiredrepresentations of the user subvocalizing text by identifying syllablesand pauses in the acquired representations, determining respectivedurations of the identified syllables and pauses, and storing thedetermined durations of syllables and pauses as the reference durationsof syllables and pauses. Optionally, the reference durations ofsyllables and pauses are dependent on a type of text.

Determining 1004 that the user phrasing signature and the referencephrasing signature fulfill a similarity condition may comprisecalculating a correlation between the user phrasing signature and thereference phrasing signature, and determining that the user phrasingsignature and the reference phrasing signature fulfill the similaritycondition if the calculated correlation exceeds a threshold value.Optionally, the correlation is calculated between the user phrasingsignature and the entire reference phrasing signature, and method 1000further comprises determining that the user has read the first textsubstantially in its entirety if the calculated correlation exceeds asecond threshold value.

Optionally, method 1000 may further comprises determining 1010, inresponse to authenticating 1005 the user, if the user is authorized toread the first text. Preferably, it is determined 1010 that the user isauthorized to read the first text based on permission informationassociated with the first text.

Optionally, method 1000 further comprises revealing 1011 obfuscatedparts of the first text in response to determining 1010 that the user isauthorized to read the first text.

Optionally, method 1000 further comprises displaying 1012 to the user asecond text in response to determining 1010 that the user is authorizedto read the first text. Preferably, the second text is displayed 1012 inresponse to detecting that the user subvocalizes a closing part of thefirst text.

Optionally, method 1000 further comprises discontinuing 1013 displayingthe first text or obfuscating 1013 at least part of the first text inresponse to determining 1010 that the user is not authorized to read thefirst text, or in response to determining 1004 that the user phrasingsignature and the reference phrasing signature fail to fulfill thesimilarity condition.

It will be appreciated that method 1000 may comprise additional, ormodified, steps in accordance with what is described throughout thisdisclosure. An embodiment of method 1000 may be implemented as software,such as computer program 804, to be executed by a processing unitcomprised in the computing device, whereby the computing device becomesoperative to perform in accordance with embodiments of the inventiondescribed herein.

The person skilled in the art realizes that the invention by no means islimited to the embodiments described above. On the contrary, manymodifications and variations are possible within the scope of theappended claims.

1. A computing device for authenticating a user of the computing device,the computing device comprising processing circuitry configured to:display a first text to the user, acquire a representation of the usersubvocalizing at least a part of the first text, derive a user phrasingsignature from the acquired representation, and authenticate the user inresponse to determining that the user phrasing signature and a referencephrasing signature fulfill a similarity condition.
 2. The computingdevice according to claim 1, the processing circuitry is furtherconfigured to acquire the representation of the user subvocalizing atleast a part of the first text by: acquiring, from one or more sensorsoperatively connected to the computing device, nerve signals capturedfrom a throat of the user subvocalizing the part of the first text, andderiving the representation of the user subvocalizing at least a part ofthe first text as a representation of the nerve signals.
 3. Thecomputing device according to claim 1, the processing circuitry isfurther configured to acquire the representation of the usersubvocalizing at least a part of the first text by: acquiring, from acamera operatively connected to the computing device, a video sequenceof the user subvocalizing the part of the first text, magnifying, byvideo processing the acquired video sequence, motions of one or morebody parts of the user, which motions are correlated with thesubvocalized part of the first text, and deriving the representation ofthe user subvocalizing at least a part of the first text as arepresentation of the magnified motions.
 4. The computing deviceaccording to claim 1, the processing circuitry is further configured toderive the user phrasing signature from the acquired representation by:identifying syllables and pauses in the acquired representation,determining respective durations of the identified syllables and pauses,and deriving the user phrasing signature as a sequence of the determineddurations of the syllables and pauses.
 5. The computing device accordingto claim 1, the processing circuitry is further configured to derive thereference phrasing signature by: identifying syllables and pauses in thefirst text, acquiring reference durations of syllables and pauses, andderiving the reference phrasing signature as a sequence of the referencedurations of the identified syllables and pauses.
 6. The computingdevice according to claim 5, the processing circuitry is furtherconfigured to derive the reference durations of syllables and pausesfrom acquired representations of the user subvocalizing text by:identifying syllables and pauses in the acquired representations,determining respective durations of the identified syllables and pauses,and storing the determined durations of syllables and pauses as thereference durations of syllables and pauses.
 7. The computing deviceaccording to claim 5, wherein the reference durations of syllables andpauses are dependent on a type of text.
 8. The computing deviceaccording to claim 1, the processing circuitry is further configured todetermine that the user phrasing signature and the reference phrasingsignature fulfill a similarity condition by: calculating a correlationbetween the user phrasing signature and at least a consecutive part ofthe reference phrasing signature, and determining that the user phrasingsignature and the reference phrasing signature fulfill the similaritycondition if the calculated correlation exceeds a first threshold value.9. The computing device according to claim 8, the processing circuitryis further configured to calculate the correlation between the userphrasing signature and the entire reference phrasing signature, theprocessing circuitry is further configured to determine that the userhas read the first text substantially in its entirety if the calculatedcorrelation exceeds a second threshold value.
 10. The computing deviceaccording to claim 1, the processing circuitry is further configured todetermine, in response to authenticating the user, if the user isauthorized to read the first text.
 11. The computing device according toclaim 10, the processing circuitry is further configured to determine ifthe user is authorized to read the first text based on permissioninformation associated with the first text.
 12. The computing deviceaccording to claim 10, the processing circuitry is further configured toreveal obfuscated parts of the first text in response to determiningthat the user is authorized to read the first text.
 13. The computingdevice according to claim 10, the processing circuitry is furtherconfigured to discontinue displaying the first text or to obfuscate atleast part of the first text in response to determining that the user isnot authorized to read the first text.
 14. The computing deviceaccording to claim 10, the processing circuitry is further configured todisplay to the user a second text in response to determining that theuser is authorized to read the first text.
 15. The computing deviceaccording to claim 14, the processing circuitry is further configured todisplay the second text in response to detecting that the usersubvocalizes a closing part of the first text.
 16. The computing deviceaccording to claim 1, the processing circuitry is further configured todiscontinue displaying the first text or to obfuscate at least part ofthe first text in response to determining that the user phrasingsignature and the reference phrasing signature fail to fulfill thesimilarity condition.
 17. The computing device according to claim 1,being any one of: a mobile phone, a mobile terminal, a smartphone, atablet, a personal computer, a laptop, an e-book reader, a computerdisplay, a television, and a media player.
 18. A method ofauthenticating a user of a computing device, the method comprising:displaying a first text to the user, acquiring a representation of theuser subvocalizing at least a part of the first text, deriving a userphrasing signature from the acquired representation, and authenticatingthe user in response to determining that the user phrasing signature anda reference phrasing signature fulfill a similarity condition.
 19. Themethod according to claim 18, wherein the acquiring the representationof the user subvocalizing at least a part of the first text comprises:acquiring, from one or more sensors operatively connected to thecomputing device, nerve signals captured from a throat of the usersubvocalizing the part of the first text, and deriving therepresentation of the user subvocalizing at least a part of the firsttext as a representation of the nerve signals.
 20. The method accordingto claim 18, wherein the acquiring the representation of the usersubvocalizing at least a part of the first text comprises: acquiring,from a camera operatively connected to the computing device, a videosequence of the user subvocalizing the part of the first text,magnifying, by video processing the acquired video sequence, motions ofone or more body parts of the user, which motions are correlated withthe subvocalized part of the first text, and deriving the representationof the user subvocalizing at least a part of the first text as arepresentation of the magnified motions.
 21. The method according toclaim 18, wherein the deriving the user phrasing signature from theacquired representation comprises: identifying syllables and pauses inthe acquired representation, determining respective durations of theidentified syllables and pauses, and deriving the user phrasingsignature as a sequence of the determined durations of the syllables andpauses.
 22. The method according to claim 18, further comprisingderiving the reference phrasing signature by: identifying syllables andpauses in the first text, acquiring reference durations of syllables andpauses, and deriving the reference phrasing signature as a sequence ofthe reference durations of the identified syllables and pauses.
 23. Themethod according to claim 22, further comprising deriving the referencedurations of syllable and pauses from acquired representations of theuser subvocalizing text by: identifying syllables and pauses in theacquired representations, determining respective durations of theidentified syllables and pauses, and storing the determined durations ofsyllables and pauses as the reference durations of syllables and pauses.24. The method according to claim 22, wherein the reference durations ofsyllables and pauses are dependent on a type of text.
 25. The methodaccording to claim 18, wherein the determining that the user phrasingsignature and the reference phrasing signature fulfill a similaritycondition comprises: calculating a correlation between the user phrasingsignature and the reference phrasing signature, and determining that theuser phrasing signature and the reference phrasing signature fulfill thesimilarity condition if the calculated correlation exceeds a thresholdvalue.
 26. The method according to claim 25, wherein the correlation iscalculated between the user phrasing signature and the entire referencephrasing signature, the method further comprising determining that theuser has read the first text substantially in its entirety if thecalculated correlation exceeds a second threshold value.
 27. The methodaccording to claim 18, further comprising determining, in response toauthenticating the user, if the user is authorized to read the firsttext.
 28. The method according to claim 27, wherein it is determinedthat the user is authorized to read the first text based on permissioninformation associated with the first text.
 29. The method according toclaim 27, further comprising revealing obfuscated parts of the firsttext in response to determining that the user is authorized to read thefirst text.
 30. The method according to claim 27, further comprisingdiscontinuing displaying the first text or obfuscating at least part ofthe first text in response to determining that the user is notauthorized to read the first text.
 31. The method according to claim 27,further comprising displaying to the user a second text in response todetermining that the user is authorized to read the first text.
 32. Themethod according to claim 31, wherein the second text is displayed inresponse to detecting that the user subvocalizes a closing part of thefirst text.
 33. The method according to claim 18, further comprisingdiscontinuing displaying the first text or obfuscating at least part ofthe first text in response to determining that the user phrasingsignature and the reference phrasing signature fail to fulfill thesimilarity condition.
 34. A computer program product comprising anon-transitory computer-readable storage medium storingcomputer-executable instructions for causing a device to perform themethod according to claim 18, when the computer-executable instructionsare executed on a processing circuitry comprised in the device. 35.(canceled)